Wire-Like Product with Composite Core and Process for Producing the Same

ABSTRACT

A wire-like product ( 10 ) for use as a feedstock in metal or plasma spraying or welding includes a metal case ( 12 ) and a composite core ( 14 ) in the case, with the core being partially sintered and containing enough metal to conduct an electrical current. To form the wire-like product, a metal tubular segment ( 20 ) is filled with a powder ( 26 ) in the absence of oxygen. Then the tubular segment is reduced in cross-section to compact the powder within it. Next the tubular segment is heated to anneal it and effect a partial sinter ( 32 ) of the powder. Another reduction in cross section breaks the partial sinter into particles and further compacts them, whereas a further heating anneals the tubular segment and resinters the particles. Repetitions of the cycle produce the wire-like product.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application derives and claims priority from U.S. provisional application 60/871,310, filed 21 Dec. 2006, which is incorporated herein by reference.

TECHNICAL FIELD

This invention relates in general to wire-like products and more particularly to a wire-like product having a metallic case and a composite core and to a process for producing the same. The core constitutes a thermo-mechanically bonded, semimetallic, composite and is contained within a malleable and ductile case, thus producing a quasicomposite wire-like product.

BACKGROUND ART

Certain manufacturing processes require weld overlays and thermal spray coatings of very specific composition that are applied by melting a feedstock and depositing it on the surface of a substrate. For example, by means of thermal spraying, a steel substrate may be provided with a corrosion-resistant coating of nickel and other constituents, even nonmetal constituents. Indeed, many thermal spraying processes call for coatings having multiple constituents, and those are best obtained from wires or other feedstock that are themselves made of multiple constituents. To this end, tubular wires exist with cores formed from powders of metals or other materials encapsulated in a metallic case, but the powders are loosely compacted and the voids between their particles contain oxygen, which can produce, in the deposit, oxides in quantities greater than desired. Moreover, the powder of the core, being loosely compacted, does not in a heat source, such as a combustion flame or an arc, mix well with the material of the case, thus detracting from the uniformity and integrity of the deposit. Also, a loosely compacted core will not conduct electricity well, if at all, so an arc will attach much more readily to the metal case than to the powder core. This renders the arc less stable and detracts from the quality of the coating.

Apart from that, wires that are formed entirely from alloys have limitations as to their constituent components. For example, a nickel-chromium alloy can contain no more than about 45% chromium by weight. Nickel, and iron as well, will accept no more than about 12% aluminum by weight. Yet greater quantities of chromium or aluminum may be desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a wire-like product constructed in accordance with and embodying the present invention;

FIG. 2 is a sectional view of the wire-like product taken along line 2-2 of FIG. 1 and showing its case and core;

FIG. 3 depicts a metal tubular segment that eventually becomes the case being filled with a powder that eventually becomes the core;

FIG. 4 shows the powder encapsulated in the tubular segment;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 4;

FIG. 6 shows the tubular segment being reduced in cross section between rolls;

FIG. 7 shows the reduced tubular section undergoing a further reduction in cross section in a die; and

FIG. 8 is a sectional view taken along line 8-8 of FIG. 7 and showing a partial sinter within the reduced tubular segment.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring to the drawings, a wire-like product 10 (FIGS. 1 & 2) for use as a consumable electrode in metal spraying or for use simply as a feedstock for an arc, combustion or plasma spraying or welding apparatus includes a metal case 12 and a composite core 14 within the case 12. The metal of the case 12 may be elemental or an alloy, but in any event, it should be malleable and ductile so that the wire-like product 10 can be bent without fracturing the case 12. The core 14 contains a metal, and should be at least 5% to 8% metal by volume. The remaining constituents of the core 14 may be a metal or non-metals, such as metalloids, carbides or ceramics. Thus, the core 14 is a composite. Whatever its constituents, the composite core 14 derives from a powder, the particles of which are highly compacted and thermo-mechanically bonded together into a dense, although partial, sinter. As such, the core 14 has no grain structure.

The process for producing the wire-like product 10 begins with a tubular segment 20 (FIG. 3) preferably of cylindrical shape. It may derive from welded tubing or seamless tubing. It is formed from the metal that is desired for the case 12 of the wire-like product 10. That metal should at the outset be ductile, that is to say, malleable and hence capable of being worked without fracturing. In this regard, the metal of the tubular segment 20 may require annealing to bring it to the desired ductability. Suitable metals for the tubular segment 20 include nickel and its alloys, stainless steel, cobalt alloys, and alloys of refractory metals. The tubular segment 20 initially should have an outside diameter preferably ranging between 5/16 and ⅜ inches and an inside diameter no less than about 20% of the outside diameter.

One end of the tubular segment 20 is swaged or otherwise closed, leaving the tubular segment 20 with a closed end 22 that is air tight and an open end 24 (FIG. 3). An inert gas is introduced into the tubular segment 20 from its open end 24. If the inert gas is argon, which is heavier than air, the tubular segment 20 should assume a generally upright orientation. In any event, the inert gas displaces the air initially in the tubular segment 20, providing an oxygen-free interior. Thereupon, with the tubular segment 20 oriented vertically or at least generally upright, a powder 26 suitable for transformation into the core 14 is introduced into the tubular segment 20 from its open end 24. The powder 26 descends into the tubular segment 20 and displaces most of the inert gas. It fills the tubular segment 20.

The powder 26 contains constituents, in particle form, that ultimately form the composite core 14 of the wire-like product 10. For most constituents the combined particles of the powder 26 should be in a size range between 300 and 40 microns. Some of the particles should be a metal, and indeed, at least 5% to 8% of the particles by volume should be metal. The remainder may be other metals, carbides, metalloids or ceramics, or a mixture of all or some of the foregoing. Once the tubular segment 20 is filled with the powder 26, its open end 24 is closed, such as by swaging, to provide another closed end 28 (FIG. 4), that is air tight thus totally encapsulating the powder 26 within the oxygen-free interior of the tubular segment 20 (FIG. 5).

With the powder 26 encapsulated within the tubular segment 20, the tubular segment 20 is reduced in size to a lesser diameter, with an accompanying extension in length. The reduction preferably occurs between rolls 30 (FIG. 6) which may be organized in multiple sets, one after the other. The reduction in size continues until the stresses produced by the deformation of the tubular segment 20, from a practical standpoint, leave it too hard to continue the reduction. The reduction by the rolls 30 tightly compacts the encapsulated powder 26 within the tubular segment 20. The reduction and compaction may also be achieved by drawing the tubular segment through a die.

The reduced tubular segment 20 and the tightly compacted powder 26 contained within it are then heated to a temperature suitable for sintering the powder 26. That temperature should not exceed melting temperature for the metal of the segment 20, yet should reach the range for annealing the metal of the tubular segment 20. Moreover, the heating should preferably occur in an oxygen-free environment, such as within a sintering furnace that contains hydrogen. Thereupon, the tubular segment 20 is allowed to cool slowly in the oxygen-free atmosphere, or quenched, depending on the metal of the tubular segment 20, to thereby anneal the tubular segment 20 while avoiding oxidation. The powder 26 converts into a partial sinter 32 (FIG. 7) and may even bond to the inside surface of the segment 20.

Next, the tubular segment 20 is forced through a die 34 (FIG. 8) to further reduce its diameter and extend its length. The draw fractures the partial sinter 32, breaking some of the bonds within it and producing particles. It simultaneously consolidates and compacts those particles all within the tubular segment 20—indeed more closely than the compaction of the powder 26 by the rolls 30. Roll forming the tubular segment 20 to a lesser diameter will achieve the same result. Irrespective of how the tubular segment 20 is further reduced in diameter, it again acquires stresses that harden it—work hardening in effect.

Thereupon, the drawn tubular segment 20 of lesser diameter and the compacted, broken partial sinter 32 within it are heated preferably in the absence of oxygen, such as in a sintering furnace, to the sintering temperature for the powder 26, yet below the melting temperature of the tubular segment 20, but nevertheless into the annealing range for the tubular segment 20. The fractured partial sinter 32 reforms as another partial sinter 32, although with different bonds. Then the tubular segment 20 and the new sinter 32 are allowed to cool slowly or quenched to again anneal the tubular segment 20.

The tubular segment 20 is again reduced in diameter by another draw or roll form. The further reduction in diameter fractures the previous partial sinter 32 into particles and further compacts them, so that the particles of the fractured sinter 32 in the tubular segment 20 are even more tightly compacted. Then the tubular segment 20 is again heated in a sintering furnace to the sintering temperature for the powder 26, yet within the annealing range and below the melting temperature for the segment 20. The heating creates another partial sinter 32. A subsequent cooling further anneals the tubular segment 20, so that it remains ductile and malleable.

Further, reduction in diameter of the segment 20 and the resulting fracturing of the partial sinter and the subsequent heating to the sintering temperature for the powder 26, yet below the melting temperature and at the annealing temperature for the segment 20, and subsequent annealing, follow in cycles, so that a total of perhaps three to five reductions and contemporaneous compactions and heating after initial reduction between the rollers 30 occur. After the last cycle, the tubular segment 20 exists in an annealed state as the case 12 of the wire-like product 10, whereas the powder 26, transformed into the partial sinter 32, takes the form of the composite core 14 in which the particles of the last partial sinter 32 are bonded together in a final, yet fractured, partial sinter 32 and along the interior of the tubular segment 20 may be diffused into the tubular segment 20 to effect a bond there as well. In short, the tubular segment 20 and powder 26 and sinters 32, by reason of the several reductions in diameter with accompanying compactions and subsequent heatings, are transformed into the wire-like product 10.

The characteristics of the core 12 depend to a large measure on its constituents. If the constituents are such that at least one is a metal that will melt at the sintering temperature for the powder 26 in the tubular segment 20, the core 14 may include an actual alloy. More likely, however, the powder 26 compacts entirely into a partially sintered mass—one in which the particles are thermo-mechanically joined together, such as by diffusion. Moreover, they may be diffused into the wall of the case 12 along the interior surface of the case 12.

The presence of at least 5% to 8% metal by volume in the core 14 enables the core 14 to conduct electricity as does the metal tubular case 12. Indeed, the high compaction brings the particles of metal in the core 14 close enough together to form an electrical conductor within the core 14. Loosely compacted powder, on the other hand, will not conduct electricity as effectively, if it conducts at all. Since the core 14 serves as a conductor, the wire-like product 10 as it is fed into an arc will have the arc attach to both the metal case 12 and to the core 14, and not just at the case 12. This provides for a more stable arc and a more uniform melting of the wire-like product 10.

In lieu of sealing each end of each wire-like segment 20, multiple wire-like segments 20 may be joined together end to end by welding in an oxygen-free atmosphere, with only the free ends of the endmost segments 20 closed.

The tubular segment 20, instead of being derived from relatively small diameter tubing on the order of 5/16 to ⅜ inches, may derive from a much larger tube, perhaps two inches in diameter, such as a tube formed in a pilger mill. After oxygen is eliminated from the interior of the larger tube, its interior filled with the powder 26, and its ends capped, the larger tube is rolled into smaller and smaller diameters with accompanying extensions in length. In so doing, the powder 26 serves as a mandrel to prevent the tube from collapsing. If necessary, the tube undergoes annealing to relieve work hardening. Eventually it becomes small enough to draw through dies to reduce its diameter even further, with each draw being preceded and followed by annealing that effects a partial sinter of the particles within the tubular segment 20.

In short, the invention resides in a thermo-mechanically bonded, semi-metallic core 14 contained within a malleable and ductile case 12 to provide a quasicomposite wire-like product 10. 

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 14. A process for producing a consumable wire for use for metal or plasma spraying or for welding, said process comprising: providing a metal tubular segment; introducing an inert gas into the tubular segment; while the interior of the tubular segment contains the inert gas, filling the metal tubular segment with a powder containing at least 5% metal by volume; reducing the cross-sectional size of the metal tubular segment containing the powder to compact the powder within it; thereafter repeatedly heating the metal tubular segment and reducing the cross-sectional size of the tubular segment, with the heating raising the temperature of the tubular segment to less than the melting temperature for the metal of the tubular segment, yet high enough anneal the tubular segment, and effecting an annealing of the tubular segment and a partial sinter of powder, the repeated reduction in the cross-sectional size of the tubular segment fracturing the partial sinter into particles that are again partially sintered in the subsequent heating; and whereby a wire is produced with a metal case and a partially sintered core having at least 5% metal by volume, but having no grain structure.
 15. The process according to claim 1 wherein the heating of the tubular segment occurs in the absence of oxygen.
 16. The process according to claim 1 wherein the tubular segment is formed from a metal selected from a group consisting of nickel and its alloys, stainless steel, cobalt alloys, and alloys of refractory metals.
 17. The process according to claim 1 wherein the powder in addition to the metal includes carbides or metalloids or ceramics or a mixture of some of all of the foregoing.
 18. The process according to claim 1 and further comprising joining multiple tubular segments together end to end.
 19. The process according to claim 6 wherein the multiple tubular segments are joined end to end by welding in an oxygen-free atmosphere.
 20. The process of claim 1 wherein the inert gas that is introduced into the tubular segment is argon.
 21. The process according to claim 1 wherein the inert gas is heavier than air and is introduced into the tubular segment at the top of the tubular segment with the tubular segment being in a generally upright orientation.
 22. The process according to claim 8 wherein the powder is introduced into the tubular segment at the top of the tubular segment and displaces the inert gas.
 23. A consumable wire formed by the process of claim
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